1. Field of the Invention
The invention relates first to a fuel pump, in particular for an internal combustion engine with direct injection, having a housing, having at least one piston which is received in the housing, having drive means, which put the piston into a reciprocating motion, having a work chamber which is defined in some regions by the piston, having an inlet conduit and having an outlet conduit, which can be made to communicate with the work chamber, having a first valve device between the work chamber and the inlet conduit and a second valve device between the work chamber and the outlet conduit, wherein the valve element of one valve device has a guide portion, which is received at least in some regions in a guide opening.
2. Description of the Prior Art
A fuel pump known on the market serves as a high-pressure fuel pump for Diesel engines of motor vehicles. The fuel is pumped at high pressure by the high-pressure fuel pump into a fuel collection line (“rail”), in which it is stored under high pressure. From the rail, the fuel reaches injection valves, which inject directly into the combustion chambers of the engine.
In the known fuel pump, the two valve devices are accommodated in a compact unit. The valve element of the valve device (“inlet valve”) between the work chamber and the inlet conduit is braced on the valve element of the valve device (“outlet valve”) between the work chamber and the outlet conduit. The valve element of the inlet valve is also guided, via a cylindrical guide peg, in a guide opening of the valve element of the outlet valve.
In the known engine, it has been found that in operation, pressure surges repeatedly occur in the inlet conduit of the fuel pump and the components located downstream of it. These pressure surges reduce the efficiency of the fuel pump. The valves are also complicated to manufacture. Moreover, regulation is difficult because of the pressure fluctuations.
Furthermore, in internal combustion engines there is the fundamental necessity of being able to suppress the pumping of fuel into the rail completely (“zero feeding”). Since a metering unit also used for the purpose, disposed upstream of the high-pressure fuel pump, even in the closed state always allows a certain leakage quantity of fuel to reach the high-pressure fuel pump, so-called zero-feed throttles are used between the metering unit and the high-pressure fuel pump, which are intended to return the leak fuel emerging from the outlet of the metering unit. By means of these zero-feed throttles, however, the starting performance of the engine is adversely affected. Without such zero-feed throttles, on the other hand, even with the metering unit completely closed, fuel would continue to be pumped from the high-pressure fuel pump to the rail.